The present invention relates to a device for monitoring the operation of a driving arrangement according to the preamble of the subsequent claim 1. As will be more closely described hereinbelow, it is preferred that the driving arrangement forms part of a manipulator, in particular an industrial robot, so that the element which can be set in motion by the driving motor forms a manipulator element of the manipulator.
The safety systems of the industrial robots of today are not sufficient for allowing people to work within the operating range of an industrial robot when the robot executes its programs. This is due to the fact that there is a large likelihood that an error in the electromechanics of the robot can cause robot movements that can injure or kill people in the vicinity of the arm system of the robot. The accidents, which can ensue, are due to the fact that the robot makes unexpected programmed movements or that the robot rushes owing to measuring or driving system errors. The injuries which can ensue in that connection are either that the robot gives the person in the operating range a strong blow or injuries caused by clamping. The cases when the head it subjected to these injuries are of course particularly serious.
Today it is presupposed that people are not allowed to be within the operating range of industrial robots when the robots execute production programs at full speed, and therefore the safety systems are today only aimed at minimizing the damages to the robot, surrounding equipment and work objects. Consequently, model based monitoring is used in order to continuously compare motor moments and motor position of the robot axles with moments and positions of a model of the robot. A more simple type of monitoring uses the control errors in the servos which are controlling the position and the velocity of the axles, and the magnitude of the moment references generated by the regulator or the current controlling devices of the motors. Furthermore, the motor currents and the motor temperature are often monitored.
When the monitoring in the robot systems of today indicate an error during the axle manoeuvre, a digital output signal is generated from a computer card to a relay, which is connected to a breaker, which disconnects the current to the motors of the robot and makes sure that the brakes of the robot are activated. The reason why these safety concepts are not sufficient is that many functions must work simultaneously in order for the motors of the robot to, with sufficiently large likelihood, always become immediately currentless in connection with a frightful situation. For instance, the software and hardware have to work in the processor which detects the condition of error. Thereupon, the software and hardware for the processor which signals the condition of error to a digital safety output also have to work, as well as the relays and breakers which are to make sure that the motor currents disappear as soon as possible.
If the error is due to the fact that the computer, which is to indicate the error, or the interface towards driving devices and measuring systems of this computer is not working, there is the risk that the error situation will not at all be detected and the driving system can make the robot rush without any control. If the error is due to the fact that a person has been clamped up between the robot and the surrounding equipment of the robot, there is the risk that the monitoring with subsequent software and hardware signalling and relay handling will take so long time that too high clamping forces have time to develop before the motors are cut off. In the same way, there is a great risk that too strong forces have time to develop between the robot and the person in case of a collision at the normal programmed robot velocity. Even though an advanced model-based collision detection is used, there is a risk that the direction of the motors will reverse too late or that some error in the software or hardware will make that the robot will not stop at all.
The purpose of the present invention is to achieve a monitoring device, by means of which a substantially improved safety in the monitoring is to be attained.
Preferably, it is intended that the risk of injuries when someone is within the range of the driving arrangement, in particular a manipulator, will be so small that it can be generally accepted to work together with a manipulator or an industrial robot.
According to the present invention, a very safe monitoring device is achieved as a consequence of the redundant driving arrangement in accordance with the subsequent characterizing part of claim 1, the high safety being attained in that the detection arrangement is designed to detect the deviations concerning the relative positions or movements between the driven element and the redundant element.
Manipulators or robots having this safety system will be able to work together with human beings, for instance during assemblage of different work shop technical products and disassembly of corresponding products for material recycling. With the inventional monitoring device, manipulators, in particular robots, can be introduced on different places in an assembly line for motor cars without having to be surrounded by fences obstructing the motor car assemblers in the operating range of the manipulators or robots. This opens up new possibilities for automatization of the assembly of private cars, lorries and busses, which today is almost entirely manual. This gives a great flexibility and the possibility to robotize afterwards an existing manual assembly line.
Further features and embodiments of the inventional device are related to in the dependent claims.